Definitely don't throw it out. Sulfur smells are common for a number of yeasts, particularly Lager yeast. With some yeasts, they become more pronounced when the yeast is stressed, often by high or low temperatures or late in fermentation as the nutrients run out.

If the fermentation is vigorous, the smell should leave the beer. Check it out before you lager, bottle or keg, if it is not gone, let it sit warm for a while longer, until it is gone.

Last edited by slothrob on Sat Dec 17, 2011 8:38 am, edited 1 time in total.

Ditto on what slothrob said. Five days is early in the process for a lager. My typical practice is two weeks at 50F degrees followed by a 48 hour diacetyl rest at ~65F degrees. This practice has resulted in clean fermentation profiles for my lagers.

Make sure fermentation is complete and all the byproducts cleaned up before you move your beer to the lagering phase. You aren't going to clean up byproducts at temperatures down near freezing.